LISA Pathfinder drops its gravity-wave-finding golden boxes

And I'm free, free fallin'

Its publicity thunder stolen by last week's announcement that the Laser Interferometry Gravitational-wave Observatory has seen the signal of the waves, the European Space Agency's LISA Pathfinder has passed what the agency calls a “major milestone”.

The LISA – Laser Interferometer Space Antenna – Pathfinder is a proof-of-concept for a hoped-for 2034 project that would put satellites on a heliocentric orbit, in a one-million-kilometre equilateral triangle.

In the meantime, the Pathfinder's mission is to test out technologies on a single spacecraft, launched on December 3, 2015. It arrived at the L1 Lagrange point on 22 January 2016, and on 16 February, the two gold-platinum cubes were released to float freely with no mechanical contact with the spacecraft.

The objective is that the cubes will eventually have no forces acting on them other than gravity. Right now, the mission boffins are applying “minute electrostatic forces” to the cubes to keep them following the spacecraft “as its flight through space is slightly perturbed by outside forces such as pressure from sunlight”, the ESA explains.

The next milestone is 23 February, when the LISA Pathfinder gets switched to science mode for the first time. That will leave the cubes and the spacecraft in free-fall.

The scientists will then run “several months” of experiments to check: how accurately the test-masses can positioned relative to each other. The boffins hope for billionth-of-a-metre accuracy.

Before you say “who needs it? We found gravity waves already” and fire off letters to The Times about the waste of money, there's a couple of reasons why LISA still matters.

First, it was planned and built long before last year's LIGO data collection run that led to last week's announcement, and launched in December 2015; second, replication matters in science.

If the 2034 LISA mission goes ahead, its million-kilometre scale will make it vastly more sensitive than LIGO – just like a 30 metre telescope sees more ordinary light than your binoculars. ®